Shower heads generally include a plurality of nozzles to provide a shower of water droplets over a large area of a user's body. It is generally desired that a shower head provide the following: efficient wetting of maximum body, sufficient pressure to wash soap suds off the body, a comfortable feel of the droplet spray on impact with the body, and conservation of water.
Spray nozzles with generic vanes are widely used in the agricultural field for spreading water, fertilizers, and pesticides. Such spraying is often performed over large tracts of land, and farmers desire to use conservative methods to dispense the fertilizers and pesticides in an efficient and economical manner. Agricultural spray nozzles use atomization techniques to break up the flow of fluids into smaller droplets, enabling the coverage of wider areas of farm land. When the droplet is too small, for instance less than 150 microns in diameter, it then becomes a misty fog and drifts away from the area that needed to be treated. Indeed one needs to be careful not to be anywhere close to such drifting, fogging, and clouding conditions.
Spray nozzles with vanes are also used widely for tank cleaning, auto wash facilities, driveway cleaning and other high-pressure applications. For such applications a higher impact force of the droplets from the liquid jet on the contact surface that is being cleaned becomes significantly important.
Spray nozzles and vanes developed for the above applications fall short of meeting the needs of bath systems, and there is clear need for an improved system that addresses this complex and challenging problem. The small droplet sizes preferred in agricultural spraying and the high droplet impact forces of pressure cleaning systems are inappropriate for shower systems. In addition, the temperature characteristics of the droplet spray are critical in showering applications, but generally have no relevance to agriculture and cleaning applications.
To apply such technology to shower heads, one has to be cognizant of the heat transfer characteristics of the water droplets and their dependence on the size of the droplets. The larger the droplet the more the mass and higher the heat flux it can hold (heat flux, Q, is defined as the amount of heat contained in the mass of material Q=mass*specific heat of the fluid*Delta T, where Delta T is the temperature difference between the inlet temperature of the jet and the ambient temperature). As the water exits from the shower head it exchanges heat with the surrounding ambient air by convection from its surface area and the bather by conduction. The larger the surface area of the droplet the greater the heat loss. Also, as a large droplet is split into large number of small droplets, the total surface area of all such smaller droplets increases, resulting in larger heat loss through convection at their surfaces. The smaller the droplet the smaller the heat flux in it and larger the heat loss. Also, the larger the droplet size the higher the heat flux in the droplet. In other words, for the same amount of flow from a shower head, larger droplets retain more heat than smaller droplets and cover lesser area to wash, whereas smaller droplets cover larger area to wash and loses more heat than the larger droplets. These two opposing properties of the droplet sizes require careful attention in selecting the droplet size to achieve the satisfactory performance from the shower head.